The present invention relates to construction of diversity handover processing apparatuses and network control systems using the same, and more particularly to a network control system for use in a multimedia network which mutually connects mobile radio network and other networks and is suitable for handling various kinds of media (voice/image/data) communicated at various speeds, and a diversity handover processor used in the system.
In digital networks in these days, widespread use has been made of a network handling radio signal transmission media such as a mobile radio network, in addition to the conventional cable network using metallic conductors or optical fibers. In connection with the mobile radio network as above, there are available the existing STM (synchronous transfer mode) network as described in xe2x80x9cMobile Communication Systemxe2x80x9d published by Ohm-sha, a PDC (personal digital cellular) or PHS (personal handyphone system) radio network described in xe2x80x9cEasy Digital Exchangexe2x80x9d published by Denki Tsushin Kyokai in which signals carried on time slots are communicated like the time-division network for communicating signals carried on time-shared time slots within a synchronized frame, or a CDMA (code division multiple access) radio network as described in xe2x80x9cEASY-TO-UNDERSTAND DESCRIPTION OF DIGITAL MOBILE COMMUNICATIONSxe2x80x9d published by Ohm-sha, pp 32 and 33 in which signals modulated with codes different for the signals are communicated. Further, a wideband CDMA (hereinafter referred to as W-CDMA) described at page 85 and ensuing pages in xe2x80x9cNikkei Electronics No. 680 published by Nikkei BP has been highlighted as a communication system which can ensure transmission and reception of various kinds of signals at various speeds, such as voice, image and high-speed data with the same quality as that in the existing cable communication network even when the mobile station moves at a high speed and is expected to be put into practice as early as possible.
On the other hand, at present, there exist various networks including a STM (synchronous transfer mode) network, a packet network as described in xe2x80x9cBasic Knowledge of Data Exchangexe2x80x9d published by Denki Tsushin Kyokai in which signals carried on packets of variable length are communicated, an ATM (asynchronous transfer mode) network) as described in xe2x80x9cE-ISDN Pictorial Readerxe2x80x9d published by Ohm-sha in which signals carried on packets of fixed length called cells are communicated or an internet as described in xe2x80x9cMastering TCP/IPxe2x80x9d published by Ohm-sha in which signals are carried on packets of variable length called IP packets and the IP packets are communicated pursuant to the procedures called intemet protocol(IP), and media of voice, image and data are communicated.
The aforementioned actual networks and communication systems have been developed and introduced independently of each other and signal forms (speed and format) and communication procedures (signal mode and protocol) differ for the individual networks and systems. In addition, characteristics of the networks are also different and therefore, there are differences in offered communication services and control mechanisms for offering the services (for example, the construction of operation system, the construction of hardware/software interfaces and the function and structure of communication application software).
The network user conducting transmission and reception of information by utilizing the networks and the provider offering the networks have an earnest desire for the elimination (or absorption) of differences in the aforementioned networks which will be conductive to communication in which the user and provider can be unconscious of the construction of the networks and the procedures and can communicate with the other party by using communication service permitting optimal communication of information whenever they want to use and whatever apparatus (terminal) they use, because this improves easiness of using the communication equipment, decreases costs and contributes to development of society. In other words, the advent of a network control system, a communication control apparatus and a method of controlling the system and apparatus has been desired which can unify the aforementioned various networks to absorb the differences in the individual radio networks and permit, through simplified control, inter-network connection that sets up mutual connection for communication. Especially, the mobile radio network such as W-CDMA is expected to be developed rapidly in the future and it is important to construct a unified network by mutually connecting various kinds of existing networks and the mobile radio network.
Handling of the signal process is sometimes required to be changed depending on differences in media and the mutual relation to other networks. Exemplarily, some of the signal process specific to mobile targets need the error correction coding process but on the other hand, in some applications, it is preferable that the coding process as above is not carried out from the standpoint of connection to the existing networks. Further, in the mobile communication, an interleave technique is employed for the sake of coping with the burst error. This technique is described in, for example, xe2x80x9cMobile Communicationxe2x80x9d edited by Masaaki Shinji, published by Maruzen Kabushiki Kaisha, according to which data processed to, for example, Reed-Solomon code are rearranged for transmission and they are reversely rearranged on the receiving side. During the rearrangement, a block memory of m rows and n, columns is used and there arises a delay in storage to the memory. Accordingly, in a service prone to be affected by the delay time, such as voice, the interleave process is not carried out in some applications even at the cost of debasement of the capability of error correction.
After the interleave process, data in a predetermined unit in the block memory is read collectively to provide burst-like data. Such data must be smoothed in accordance with a timing in a mobile radio network when transferred to that network and therefore there needs a buffer for receiving such a burst signal as above. When interleave is not carried out, no burst signal is generated and only control timed to the mobile radio network may be carried out.
Further, when down-load of file is effected during access to an internet, unidirectional traffic from the network to the terminal takes place and when it is presupposed that the same traffic passes bidirectionally, resources of one of the network and terminal becomes sometimes unwanted. Preferably, the use rate of individual media will be determined statistically to permit apparatus and network having the construction commensurate with the determined use rate to be constructed. But media used by users change day by day and the situation is further changed by mutual connection with other networks. Accordingly, when connection to various kinds of networks is taken into account, it is necessary that various kinds of service can be handled by way of individual connections and impairment of economical advantage can be prevented.
In diversity handover, a process is executed in which quality evaluation is effected in a unit of packet and a packet of good quality is selected. On the other hand, for the purpose of improving the line efficiency between the base station and the network control system, it is conceivable that the base station first stores a plurality of CPS (Common Part Sublayer) packets in a payload of one ATM cell and then transmits them to a network. In this case, the network control system cannot perform the diversity handover process unless the ATM cell is decomposed in a unit of packet to generate one ATM cell every CPS packet. The reason for this is that in the diversity handover, the quality evaluation being carried out in a unit of packet. Accordingly, in the network control system, the number of ATM cells is increased by the number of CPS packets and the process in the network control system is loaded several times as compared to the process of ATM cells in the communication line, with the result that a switch used in the network control system is required to have higher efficiency.
In the case of communication between conventional fixed telephones, the speech path is not changed in general, during communication once a call is connected. In the case of mobile communication or network, however, a mobile station is movable and a base station with which the mobile station communicates can be changed even after a call is connected. As the base station is changed, a process for addition and deletion of communication path takes place in the communication control system accommodating the base station. Further, in the CDMA system, for the purpose of performing the diversity handover process, a plurality of speech paths must be maintained or deleted in respect of one mobile station in the communication control system. As described above, disadvantageously, the process for addition or deletion of speech path must be carried out more frequently in the CDMA mobile system than in the fixed telephone. Further, since speech paths which are larger in number than mobile stations to be connected must be maintained, resources in the communication control system must be utilized efficiently, that is, deleted or erased speech path resources must be reused efficiently at once. An object of the present invention is to provide a diversity handover processing apparatus which can realize the aforementioned unification of a mobile radio network and the existing network or mutual connection therebetween and a network control system using the diversity handover processing apparatus.
According to an aspect of the present invention, a diversity handover processing apparatus comprises a shared buffer memory for storing signals inputted from a communication terminal and converted into ATM cells, a combining/copy information table for storing connections necessary to selective combining or copy of the ATM cells received from the shared buffer memory, a combining/copy controller for reading information concerning connections in the combining/copy information table in respect of the communication terminal, a shared buffer memory handling section for designating addresses contained in the information read by the combining/copy controller, the addresses being of the shared buffer memory and concerning the connections, and controlling read operation of ATM cells designated by the addresses, and a combining/copy processor for performing selective combining or copy of the ATM cells read out of the shared buffer memory in connection with the communication terminal.
According to another aspect of the present invention, a network control system comprises a plurality of interfaces for converting signals from a communication terminal into ATM cells added with header information indicative of a predetermined destination, an ATM switch for delivering the ATM cells inputted from the interfaces on the basis of the header information of the ATM cells, and a diversity handover processing apparatus for applying a combining or copy signal process to the ATM cells inputted from the ATM switch in accordance with a state of the communication terminal and transmitting the processed ATM cells to the ATM switch.
With the above construction of the invention, signals from the communication terminal can be converted into ATM cell forms and an ATM cell of good quality can be selected from the ATM cells received through the ATM switch to realize the combining/copy or so-called diversity handover process.